- Evaluation of Inter rater Reliability for Movemen
t and Posture Observati ons of workers in an Aud
io Compact Cassette Plant
Dararat Techakamolsuk Pornchai Sithisarankul
- INCIDENCE OF WORK RELATED MUSCULOSK
ELETAL DISORDERS : social security office, MinistryofLaborandsoci al wel f ar e 1 9 9 8
SEVERITY LIFTING HEAVY OBJECTS INJURIES/ ILLNESS FROM WORKINGIN THE SAME POSITION CONSTANTLY
DEATH 1 3
PERMANENTPARTIAL
DISABILITY
19 15
TEMPORARYDISABILITY ( MORE
THAN 3 DAYS
1,432 527
TEMPORARYDISABILITY( NOTMORE THAN 3
DAYS)
10,134 2,522
Ergonomics is defined as the study of the interactionbetween workers and the equipments being used and theenvironments in which they function
Ergonomics is centered on the person
The equipment itself can be important if the person must operate, service, install, and/or repair that equipment
The application of this knowledge to the workplace is essential to order to enhance productivity and to increase the social responsibility of the firm
Laboratory and epidermiologic studies : association between various work-related musculoskeletal disorders and
1.exposure to highly repetitious or static work
2. work requiring high force3. Non –neutral position or postures4. awkward postures5. localized contact pressure6.vibration 7. cold
The ergonomic exposures have been assesses by questionnaires PROBLEM :the reliability of self-reported physical exposures have been mixed.
Observational methods continue to be used commonly, especially to assess ergonomic stresses.
MATERIALS AND METHODSSubjects - four observers (A,B,C and D)
indepentdently evaluated 23 workers using a procedure that included
observations of 27 movements and 11 postures from the adapted observational check list
around april 2000in an audio compact cassette plant, area
of molding department , audio assembly area and audio package department
MATERIALS AND METHODSInstrumentThe ergonomics exposure data : on a onsite observation check list
information to identify each job observed (plant, department , operation number )
day of evaluation the picture 1-28 for evaluation
of movement and work posture
All of them were evaluated in the topic of 1. Repetitions
very often - twice or more in one minute
often - once for each period of 1-3 minutes
occational - once in more than 3 minutes
2. speed
Very fast - close to the maximum speed that can be repeatedly performed by the worker for a given manufacturing operation.
Moderate - is the speed that most resembles natural body movements
Slow - is a speed that is notoriously lower than the moderate
3. Forceful exertion
Much - similar to the maximum value that can be maintenanced during one half of a minute
Moderate - similar to the maximum that can be maintenanced during a period lasting from 1 to 3 minutes
Little - any force that can be maintained for more than 3 minutes
All were evaluated in the topic of 1.Posture time
( accumulated time during daily journey) :
Between 0 and 1 hour
Between 1 and 3 hour
More than 3 hours
2. Forceful Exertion
Much - similar to the maximum value that can be maintenanced during one half of a minute
Moderate - similar to the maximum that can be maintenanced during a period lasting from 1 to 3 minutes
Little - any force that can be maintained for more than 3 minutes
3. Kind of force applied :
• Pushing • Pulling • Twisting the body
Each task was observed for each cycle at least 3 minute
watching all tasks in each cycle at least once time before beginning to count and record specific movements and postures
Data analysis methods
Interrater agreement on the frequency per cycle , speed of motion and forceful exertion of each of the the 17 movements
Interrater agreement on the accumulated time, forceful exertion and kind of force applied of each of the 11 postures
Data analysis methods
evaluated using statistical approaches : proportion of agreement and kappa
performed using SPSS 9.0 for window
Measuring agreement
The simplest calculation : proportion of agreement( the sum of the frequencies along the main diagonals of contingency table)
Kappa ( k ) is a measure of agreement that does account for chance
kappa substracts the proportion of agreement that could be expected by chance alone from the observed proportion of agreement
Example … topic…. Repet itionof pi c . 2
Observer A Very oftenObserverB
Often Occational TotalVery often 9 1 0 10
Often 2 9 1 12
Occational 0 1 4 5
Total 11 11 5 27
2227 08148 8Percent agreement = / = . ( % %148
%%%%%%%% %%%% %% %%%%%% % % %= 9 .44
11*10 27 407very often = ( ) / = . 12*11 27 444often = ( )/ = . = ( 5 * 5 )/ 2 7 = 0 .9 3 944 27 035proportion of the total . / = . - 081035 1calculate the agreement as ( . . ) / (
- 035 070. )= . = KAPPA
Measuring agreement
Kappa has a maximum of 1.00 when agreement is perfect
a value of zero indicates no agreement better than chance
negative values show worse than chance agreement which is unlikely
Kappa ( k ) Value of k
Strength of agreement <0.20
Poor 0.21 - 0.40 Fair 0.41 - 0.60 Moderate 0.61 –0.80 Good 0.81 –1.00 Very good
Mathematics for kappa
Kappa is calculated from the observed and expected frequencies on the diagonal of a square table frequencies
n observations in g categories : the observed proportional agreement is g
P o = i =1 f Ii / n
Mathematics for kappaf ii is the number of agreements for
categories i : The expected proportion of agreements by chance is given by g
P e = i =1 rici / n2 The index of agreement, kappa, is
given byK= Po – Pe / 1 – Pe
The approximate standard error of k is Se(k )= P o( 1- Po ) / n(1 – Pe)2
95% confidence interval K - 1.96 Se(k ) to k + 1.96 Se(k )
RESULTSIn the part of movement observation ranged
from 57% for close elongated pinch ( from the issue of exerted force)to 100% for elbow flexion, neck flexion ,lateral rotation and etc.
For the part of posture observation, interrater agreement ranged from 83% for kneeling ( in the issue of accumulative time) to 100% for standing, awkward, standing with raising arm above shoulder and etc.
RESULTS
For all of the data, kappa calculation was not shown much different, ranged from fair to very good of both observation on movement and posture and seem to be similar when comparing within two observers as the first observer (A) was a standard
DISCUSSION AND CONCLUSION
The work observed in this study was fast- paced, and the workers combined several movement and postures into one continuous, fluid movement
gross body motion seem to be easier to observed and the result in better agreement than smaller motions
the extreme postures were much easier to noted when comparing with slight deviation from neutral.
DISCUSSION AND CONCLUSION
. Well preparing of check list and selected each of all movement and postures( picture 1- 28) is so important
training all observers
needed furthur to evaluate in all issue of that movement and posture.
The real purpose
for safety officer of the industries( the well trained observers)
estimating risk factors and potential levels + interpreting the data of the self report musculoskeletal problems or diseases
the adapted check list for movement and posture observation
The best ergonomic exposure assessment method ???appropiateness for use in the large
populations at reasonable cost the versatility to estimate a variety
of exposure factors the ability to represent the
exposure of the job over appropiate length of time
Reliabilty and validity of the method
interrater reliability of observation
operational definition simple and clear
long and multiple training sessions number of observation the level of detail maybe longer observation periods
and repeated observations.